1. Field of the Invention
The present invention relates to a drawing device that generates a force for assisting manual one-way movement of an opening/closing body such as a sliding door, a folding door or a drawer.
1. Related Art
A sliding door is sometimes provided with a drawing device that generates an assisting force in a closing direction for the sliding door that moves in the closing direction. A typical drawing device is called a self-closing device, and when the sliding door is moved manually along the guide rail in the closing direction and reaches a certain point, a biasing force in the closing direction by the elastic member is exerted on the sliding door. Then, the sliding door moves automatically in the closing direction and stops at a fully closed position (see, for example, Japanese Patent Application Laid-open No. 2008-285933).
On an upper part of a frame, a guide rail is attached that extends in the moving direction of the sliding door. The drawing device is held in the guide rail and can slide in the longitudinal direction of the guide rail by rollers. The sliding door suspends from the drawing device. When the sliding door is pushed manually and moved in the closing direction, the drawing device also moves in the closing direction. There is a pin fixed to the guide rail. When the drawing device moves in the closing direction and reaches a predetermined position, a slider of the drawing device catches the pin. Then, lock between the slier and a base of the drawing device is released and the base moves in the closing direction toward the slider by the elastic member of the drawing device. As the slider holds the pin, it does not move, and hence, the base moves in the closing direction. As the sliding door suspends from the base of the drawing device, the sliding door moves in the closing direction in accordance with movement of the base in the closing direction.
In order to prevent strong collision of the sliding door against the frame or door stop by the biasing force of the elastic member, the drawing device is provided with a damper. In the Japanese Patent Application Laid-open No. 2006-200300, there are two rotary dampers provided in the drawing device, which generate damping forces in accordance with the strength of the biasing force of the elastic member thereby to smooth movement of the sliding door. That is, at the initial operation time when a large biasing force acts on the drawing device, the two rotary dampers are operated to increase the damping forces, and immediately before the sliding door is closed with a small biasing force that acts on the drawing device, one of the rotary dampers is operated to reduce the damping force.
In the drawing device as disclosed in Japanese Patent Application Laid-open No. 2006-200300, on a drawing frame of the drawing device, the two rotary dampers are mounted with a space created therebetween in the longitudinal direction, and the rotary dampers have pinions. The guide rail mounted on the frame has a rack. When an operating member mounted on the sliding door operates a catch member, a pulling coil spring operates to move the drawing frame in the closing direction relative to the guide rail, and at the same time, the pinions move on the rack. Then, the rotary dampers rotate, and a predetermined damping force can be obtained. When the drawing frame moves further, the first pinion gets out of the rack, the damping force is reduced accordingly and the sliding door closes smoothly.
In the above-mentioned drawing device, the two rotary dampers are aligned in the moving direction of the sliding door in order to obtain predetermined damping performance. It is necessary for one of the rotary dampers which is positioned to the closing side of the sliding door to have high durability since it is operated constantly from the time when the drawing device starts to the time when the sliding door is closed completely.
Then, the present invention has an object to provide a drawing device that is capable of generating a damping force in accordance with the strength of a biasing force of the elastic member without increasing the durability.